Kenya's minister for internal security, who once served as the country's vice president, and his deputy are among six people who died when a police helicopter crashed near the capital Nairobi, according to Kenyan officials.
Minister George Saitoti and his deputy, Orwa Ojode, were killed in the crash, Vice President Kalonzo Musyoka said on Sunday.
Two pilots and two bodyguards were also killed, officials said.
Saitoti, 66, was a candidate in next year's presidential election and a key figure driving his country's fight against al-Qaeda-affiliated al-Shabab fighters in neighbouring Somalia.
Following news of his death, al-Shabab released a message on its Twitter account, saying: "[Al-Shabab] welcomes the death of the evil minister upon whose authorisation thousands of Muslims suffered both in Somalia and in Kenya."
"For the hundreds of Muslims killed and displaced by Kenya's brutal invasion, Saitoti's death is but a droplet of justice in a sea of oppression," the group tweeted.
The crash occurred in the Ngong hills on the outskirts of the Kenyan capital, a police source told AFP, adding that the reason for the crash was not immediately clear.
Raila Odinga, the Kenyan prime minister, said investigations into the cause of the crash had started and that the cabinet would hold a special session on the incident.
"This is a terrible tragedy that has struck our country this morning. Nobody knows exactly the cause of this accident. That is why experts will carry out investigations," Odinga told reporters at the scene of the crash.
"We will do everything possible to ensure we find we find out the cause of this accident, but for now it is just an
Al Jazeera's Peter Greste, reporting from Nairobi, said that the area was notorious for bringing down aircraft and that the weather at the moment was quite overcast.
"It wouldn't be surprising if there was some sort of pilot error or mechanical failure," said Greste.
Witnesses at the scene reported seeing charred bodies, while images of the crash scene showed the helicopter reduced to twisted metal.
|Saitoti was a leading voice against al-Shabab [Reuters]
Saitoti, who was a long-serving vice president under former president Daniel Arap Moi, was an ally of President Mwai Kibaki.
He often visited the scenes of grenade attacks carried out by al-Shabab inside Kenya in retaliation and had vowed that Kenya would crush the group.
Our correspondent said he suspected that some conspiracy theorists would not accept that Saitoti's death appeared to have been accidental.
"Saitoti was one of the most powerful and prominent politicians in the country... Inevitably [some Kenyans] will see this as a political assassination because of his powerful position," said Greste.
"But I think we need to be very careful about implying that he might have been assassinated ... Clearly we have got to wait and see what the investigation throws up before we look in that direction."